The invention relates to a process and to an apparatus for coating, and in particular for painting, individual objects or small-series batches with a small quantity of paint with the aid of a plurality of atomizers, arranged one behind the other.
In order to supply different atomizers for example in a spray booth, it is known for a so-called xe2x80x9ccircular pipelinexe2x80x9d to be laid along and/or around the booth. This circular pipeline usually begins at a paint-storage container, from which the paint material is fed into the circular pipeline with the aid of a delivery pump, and it terminates likewise at said paint-storage container, into which the pumped-round paint flows back again. The line is equipped with the fittings, necessary for proper operation, for maintaining a constant paint pressure.
Branching off from said circular pipeline to each spray point are branch lines, by means of which manual spray guns or else automatic paint atomizers may be supplied. If a multiplicity of circular pipelines for different colours are provided in parallel alongside one another, then the individual colours may be routed via a so-called xe2x80x9cautomatic colour changerxe2x80x9d, which feeds the respectively required colour to the atomizer via an individual line. The majority of these colours, which are usually processed in an installation, are so-called standard colours.
If, however, in contrast to the colour range which is supplied as standard, individual colours are to be made available for a short period of time, for example in special series, then the special colour has to be exchanged with the standard colour in one of the circular pipelines present or an individual circular pipeline solely for special colours may be supplied, in which a quick change of the colours introduced is then possible.
It is often also desired to paint merely individual workpieces, or very small quantities of workpieces, with a special colour.
For this purpose, it is known for one of the conventional circular pipelines to be filled with a special colour, there being cases in which the quantity of paint which is necessary for filling the line is larger than is necessary for actually painting the workpiece.
It is thus also known for containers for extremely small quantities to be positioned at different spray points along a spray booth, in order that the atomizers need only be supplied with short line sections. This alternative to the laborious filling of a circular pipeline for a short period of time is customary in many cases.
The object of the invention, irrespective of the basic conditions, is to specify a particularly expedient process and an apparatus for coating, and in particular for painting, individual objects or small-series batches with small quantities of paint at a plurality of atomizers arranged one behind the other, with the result that only the quantity of paint which is actually required and, in addition, a minimal, system-induced residual quantity are necessary.
In order to achieve this object, the invention provides that only the quantity of paint which is required overall and, in addition, a minimal residual quantity are introduced into the main supply line, irrespective of the length and of the actual capacity thereof, e.g. a paint quantity less than the volume capacity of the main supply line, and that the quantity of paint which is located in the main supply line is forced, with the aid of at least one pig, which is subjected to the action of a pushing medium, to the atomizer or atomizers which is/are still to be operated, and is fully, or virtually fully, discharged there.
The quantity of paint which is required is known in principle and the same applies to the capacity of the lines. Taking account of these variables, only this amount of coating medium is fed into the main supply line and either applied to the workpiece or workpieces at one or more atomizers or is only applied when the pig and the pushing medium moving it are already located in the main supply line, It is thus possible for the coating medium introduced to be used up completely without considerable residual quantities having to be discarded and disposed of.
The atomizers are usually located at the free end of branch lines, the other end of which is arranged on a colour changer, through which the main supply line is guided.
In order for the contents of said branch lines likewise to be fully utilized, a development of the invention provides that, even prior to completion of the coating, the contents of the branch line are emptied under pressure likewise with the aid of a pig in the direction of the atomizer or, following completion of the coating, are emptied under pressure in the direction of the colour changer and main supply line.
In order to carry out the process, metering and/or control and/or measuring devices are provided to a sufficient extent, these measuring the essential parameters of the volume flow at the respectively relevant points and controlling the apparatus.